Aspects of the invention relate to a method and apparatus for determining the phase compositions of a multiphase fluid flow, in particular, although not exclusively, to a method and apparatus for determining the dryness of wet steam.
The use of steam as a heating medium in industrial processes is very widespread. Most process and heating steam systems use saturated wet steam which is a two-phase fluid comprising vapour as a first phase and condensate as a second phase.
It is often necessary to know the dryness, or quality, of the wet steam. Steam quality is the percentage of the mass of the fluid that is vapour, and therefore saturated steam has a steam quality of 100% and saturated liquid has a steam quality of 0%.
Some industrial processes have particular requirements regarding steam quality. For example, in sterilisation systems the steam quality must be between 95%-100%. This is set-out by standard BS EN 285 which specifies the requirements and relevant tests for large steam sterilisers primarily used in health care. Currently, steam quality is typically measured using throttling calorimetry. An example of an apparatus and method for measuring steam quality using a throttling calorimeter is disclosed in GB 1906 12,615. Whilst throttling calorimetry can be used to successfully determine the quality of steam, it is a time-consuming process and the apparatus is relatively complicated.
It is therefore desirable to provide an improved method and apparatus for determining the phase compositions of a multiphase fluid flow.